[gdal-dev] THANK YOU!

[David Verbyla]

OK..I figured it out that the layername is not the layer object,
it is the name property of the layer object and has to be enclosed
in double quotes.

For example:
test = ds.ExecuteSQL('select * from "three_points"  where Class IN (1,3)
')  #returns 2 of 3 point features

http://www.gdal.org/ogr/ogr_sql.html would be more helpful if there were
some Python examples...
for example:
it is not clear from the first example that polylayer is the name of the
layer, not the layer object, and needs to be enclosed in
double quotes:

SELECT * FROM polylayer

Thanks!

Dave Verbyla

On Tue, Feb 5, 2013 at 12:50 AM, Homme Zwaagstra <hrz at geodata.soton.ac.uk>wrote:

> Dave,
>
> Try the following modified version of your code snippet below. Note
> that `ExecuteSQL` expects a simple SQL string - it does not do any
> interpretation of local python variables! See
> http://www.gdal.org/ogr/ogr_sql.html for more information on the SQL.
>
>     import os
>     from osgeo import ogr
>     ogr.UseExceptions()         # if something goes wrong, we want to know
> about it
>     driver = ogr.GetDriverByName('ESRI Shapefile')
>     ds = driver.Open('three_points.shp', 0)#0--read-only
>     layer = ds.GetLayer()
>     layerName =  layer.GetName() #returns string 'three_points'
>     test = ds.ExecuteSQL('select * from "%s"' % layerName)
>
> Cheers,
>
> Homme
>
> On Tue, Feb 05, 2013 at 12:39:50AM -0900, David Verbyla wrote:
> > I am not understanding some key aspect of this function.
> > For example:
> > #three_points.shp contains
> > #Class, Point_X, Point_Y
> > # 1,301665.4,1701522.8
> > # 2,302240.3,1701992.1
> > # 3,301559.8,1701112.1
> > import os
> > from osgeo import ogr
> > driver = ogr.GetDriverByName('ESRI Shapefile')
> > ds = driver.Open('three_points.shp',0)#0--read-only
> > layer = ds.GetLayer()
> > layerName =  layer.GetName() #returns string 'three_points'
> > test = ds.ExecuteSQL('select from layerName *')
> > print type(test) #returns <type 'NoneType'>
> >
> > test = ds.ExecuteSQL('select from layer.GetName')
> > print type(test) #returns <type 'NoneType'>
> >
> > ds.ExecuteSQL('select from layerName where Class > 0')
> > print type (test) #returns <type 'NoneType'>
> >
> > Thanks in advance.
> >
> > Dave Verbyla
> >
> >
> > On Mon, Feb 4, 2013 at 11:59 PM, Homme Zwaagstra <
> hrz at geodata.soton.ac.uk>wrote:
> >
> > > Hello Dave,
> > >
> > > On Mon, Feb 04, 2013 at 06:32:11PM -0900, David Verbyla wrote:
> > > > I am trying to figure out the syntax for .ExecuteSQL using Python
> ogr.
> > >
> > > I have successfully been using `DataSource.ExecuteSQL` from Python
> > > using gdal 1.9.0.
> > >
> > > > For example:
> > > > fireLayer.SetAttributeFilter(None) #returns all 2623 polygons
> > > > fireLayer.SetAttributeFilter(" FIREID < 75 ") #returns 4 polygons
> > > >
> > > > I am trying to get the same results using the ExecuteSQL:
> > > > testLayer = dataSource.ExecuteSQL("select * from fireLayer")
> > > > type(testLayer) #retuns NoneType
> > > > testLayer = dataSource.ExecuteSQL("select * from fireLayer where
> FIREID <
> > > > 75")
> > > > type(testLayer) #retuns NoneType
> > >
> > > `None` seems to be returned when the SQL does not generate any
> > > features.  Therefore the only thing I can think that might be wrong is
> > > that the identifier `fireLayer` in the SQL above is not matching the
> > > layer name in `dataSource`. Amending to the following *should* work:
> > >
> > >     dataSource.ExecuteSQL('select * from "%s"' % fireLayer.GetName())
> > >
> > > Cheers,
> > >
> > > Homme
> > >
> > > > Thanks in advance.
> > > >
> > > > Dave Verbyla
> > > >
> > > > On Sat, Dec 22, 2012 at 7:17 AM, David Verbyla <dlverbyla at alaska.edu
> >
> > > wrote:
> > > >
> > > > >
> > > > > I am a newbie to OGR/OSR using Python 2.7.2, please excuse my
> > > ignorance:
> > > > >> I am trying to find the distance to the closest polygon for each
> > > point.
> > > > >> Is there a more efficient way than simply computing the distance
> to
> > > all
> > > > >> polygons for each point?  For example:
> > > > >>
> > > > >
> > > > > nPts = pointsLayer.GetFeatureCount()
> > > > > nPolys = polysLayer.GetFeatureCount()
> > > > >
> > > > > for pt in range(0,nPts):
> > > > >       minDist = 1000000
> > > > >       pointFeature = pointsLayer.GetFeature(pt)
> > > > >       for poly in range(0,nPolys):
> > > > >             polyFeature = polysLayer.GetFeature(poly)
> > > > >             Dist = pointFeature.GetGeometryRef().Distance(
> > > > > polyFeature.GetGeometryRef() )
> > > > >             if (Dist < minDist):
> > > > >                   minDist = Dist
> > > > >       print (pt,minDist)
> > > > >
> > > > > Thank you.
> > > > >
> > > > > Dave Verbyla
> > > > >
> > >
> > > > _______________________________________________
> > > > gdal-dev mailing list
> > > > gdal-dev at lists.osgeo.org
> > > > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> > >
> > > --
> > > Homme Zwaagstra
> > > GeoData Institute
> > > University of Southampton
> > >
> > > Tel: +44(0)2380 59 8709
> > >
>
> --
> Homme Zwaagstra
> GeoData Institute
> University of Southampton
>
> Tel: +44(0)2380 59 8709
>
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